For Members Only An Apparatus for the Evaluation of Web Heating Technologies: Development, Capabilities, Preliminary Results, and Potential Uses

It is generally acknowledged that web preheating improves press performance by lowering the viscosity of the water internal to the web. Improvements in web preheating translate into immediate improvements in press efficiency. Steam boxes are the universally accepted devices for preheating the web. However, there is little or no accessible literature on how best to employ steam boxes. The Institute of Paper Science and Technology, IPST, has designed, built, and tested an apparatus for evaluating web heating technologies. The apparatus consists of a sled, a track for the sled, a steam box, and a vacuum box (if specified). A single instrumented sheet is mounted on the sled, and the sled is propelled, at paper machine speeds, down the track under the steam box. The intent is to expose the instrumented sheet to the same thermodynamic and aerodynamic conditions that a continuous web experiences on a paper machine. Preliminary experiments demonstrated that the apparatus is an effective tool for investigating, under dynamic conditions, most factors affecting steam box performance. The experiments also show that a number of variables affect the ability of the steam box to thoroughly heat the web. One of the most significant variables is vacuum level at the underside of the sheet. The apparatus can be used to investigate both web heating problems on specific paper machines and fundamental processes in web heating